American Motorcycle Dealer AMD 230 September 2018 - Page 56

TECH EXTRA Whip Test Tensile different pull rates until failure occurs. This test literally stretches a brake hose assembly until it either pulls off one of the crimped end fittings, or the hose itself fails by tearing or fraying, whichever occurs first. The hydraulic brake hose assembly must withstand a pull of 325 lbs during a slow pull test and 370 lbs during a fast pull test, without separation from its end fittings. Designing the crimp joint to meet this specification must not compromise the constriction test due to over- crimping the fittings to increase pull-off. This is one of the most difficult of all the tests to pass due to the enormous stresses that the hose is subjected to. This is especially true for stainless steel braided lines which experience metal fatigue when being bent continuously on a flexing machine at 800 rpm for a grueling 35 hours. For an onlooker, the brake hose looks like an airplane prop, a mere blur, and failures usually occur on the hose at or near the stationary end fitting. The assembly’s hose couplings are mounted on the machine with a very specific amount of slack added to the line, depending on the length of the test sample. Each end is then locked down with no ability to spin, which would otherwise reduce the stresses on the assembly. The brake hose assembly is then pressurized with water and monitored via pressure sensors. During the duration of this test, if there is any detection of a drop in pressure from the fittings or hose, it is deemed a failure. This test ensures that the fittings and hose are designed and manufactured robustly enough to perform on the vehicle over the long term without mechanical failures from vibration, movement or flexing. Water Absorption Tests Because brake hose assemblies are constantly being subjected to rain, splashing water, and steam from hot exhaust tubes, this test’s recipe calls for three hose assemblies to be completely immersed in distilled water at 185° F for 70 hours. Within 30 minutes after removal from the water, they must be subjected to, and pass, the previous three tests again - Tensile, Burst and Whip. Due to the possibility of the hose materials being mildly hydrophilic, water may be absorbed and its physical properties may be altered. This may lead to the assembly experiencing more difficulty passing these three tests. High Temperature Impulse Test This is a rather intense test designed to ensure the durability of the brake hose assembly by simultaneously subjecting it to heat and pressure cycling. For approximately 5 hours, an assembly Whip Burst Strength The Whip Test is one of the most difficult of all the tests to pass due to the enormous stresses that the hose is subjected to Burst This is a fun and sometimes loud test. The hydraulic brake hose assembly must withstand water pressure of 4,000 psi for two minutes without rupture. Popular motorcycle brake hoses that have an I.D. of 1/8” must be tested to 7,000 psi. Hoses need not be burst to pass this test, but it may be noted that some 1/8” hoses with high tensile stainless steel or aramid fiber constructions may exceed 25,000 psi before rupturing, and when they do, they do it with a bang! 56 AMERICAN MOTORCYCLE DEALER - SEPTEMBER 2018